The Dahl/Rapp salt sensitive (S) and its control the salt resistant (R) rats have been extensively used to study the pathobiology and genetics of salt sensitivity in the rat. The S isoform of the sodium-calcium exchanger (SNCE) differs from the R isoform (RNCE) in an area for alternative splicing that is in the cytoplasmic loop. The two isoforms differ at position 218 where there is an isoleucine to phenylalnine substitution in the SNCE. This difference is proposed to underlie the finding that PKC upregulates the NCE in R but not S afferent arterioles and mesangial cells. The goals of this proposal are: 1) to clone the exchanger from S, R and SD rats afferent and efferent arterioles, express the isoforms in OK-PTH cells and evaluate their regulations, 2) to examine the activity of the NCE in afferent and efferent arterioles of the three rat strains maintained on low and high Na diet, and evaluate the role of the exchanger in the control of cytosolic Ca and vessel diameter, 3) to examine the mechanisms of translocation from cytosol to the plasma membrane of isoforms of the NCE from the three rat strains and the role of phosphorylation, PKC and other kinases in this process, and 4) to examine by mutagenesis experiments the role played by amino acid differences at position 218 and at alternative splice sites in the function of isoforms of the NCE.